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Breast Storage Capacity

posted Jul 5, 2014, 6:13 AM by Carolyn Honea, IBCLC, CLC   [ updated Mar 19, 2018, 5:03 AM ]
Do you ever wonder why some breastfeeding moms and babies seem like they can happily go 3, even 4 hours between feedings while other babies are hungry for feedings every 1.5-2 hours? Or why some chunky babies are sleeping through the night while other moms lose their milk supply and baby stops growing when baby sleeps through the night?

The answer is usually basic anatomy. Something lactation professionals refer to as Breast Storage Capacity. You may be under the impression that if you have a healthy milk supply your baby's sucking at the breast will turn on a milk faucet that lets out as much milk as baby is willing to drink. In reality, the milk your baby gets at a feeding has been gradually building up in your breasts ever since his previous breastfeeding. The amount of milk your breasts can "store" between feedings is called your Breast Storage Capacity. It is determined by the number of
mammary glands - also called lobules and ducts - that are in your breast. Studies show some women have as few as 3 milk lobules/ducts and others as many as 15. As a result the amount of milk that can fit in a woman's breasts varies - anywhere from 2oz to 5oz combined is average but some women can store as much as 10 oz in one breast (this is very unusual). Think of it this way: your breasts are like drinking cups - some women have a shot glass and some have a tumbler. Either way, baby can take in as much milk as he needs in day (average 27oz from 1-9 months) but a baby utilizing a shot glass will have to return to the "tap" much more frequently than a baby drinking from a tumbler.
Its even more amazing than this. When baby empties your "cup" of breastmilk, your body knows it and sends signals to turn the faucet on higher - to speed up milk production and more quickly refill the cup for the next feeding. However, when milk sits in your "cups" for extended periods (i.e. sleeping through the night) or if your body senses the milk is nearing the full capacity it can store - an opposite signal is sent - slow down milk production. Your body is constantly interpreting baby's milk removal and your breast fullness as an indication of whether to make more or less milk, and whether to make it quickly or slowly. Your body aims to keep your milk supply just right for baby's needs through a genius interaction between your milk storage capacity and baby's feeding demands.
At this point, you may be wondering… Am I a shot glass or tumbler? How can I tell?  Breastmilk storage capacity is not always related to breast size (some women simply carry more fat in their breasts, not necessarily more milk lobules/ducts where the milk is stored), so looks can be deceiving. The good news is, your baby will tell you

At first, newborn feeding patterns are all over the place since newborns have such tiny tummies (the size of a marble at birth!), so no matter how abundant your milk, feedings will be small and frequent. During the first days and weeks you will get to know your baby's feeding cues - the universal language of babies that communicates their need to nurse for hunger, thirst and comfort. Those frequent feedings in the first two weeks play a very important role in activating your milk ducts. If all the ducts aren't "activated" by frequent feedings the first two weeks, your body won't be able to utilize your maximum storage capacity later. As you respond to your baby's feeding cues, letting her guide the way and set your milk supply, she will eventually settle into a rhythm that fits her metabolism, personality, and your breast storage capacity. After 4 weeks, you may be able to identify your breastmilk capacity by looking at baby's feeding frequency, your pumping output (only applicable if you pump regularly), and baby's milk transfer at the breast (determined by a breastfeeding professional by weighing baby before and after feeding):

Average milk intake (25-30oz) stays constant from 1-9 months of age, so most babies don't drop feedings over time unless mom has a tumbler size storage capacity. However, older babies do tend to move nighttime feedings more into the daytime - a blessing for sleep deprived mothers everywhere! Babies also get faster and more efficient at breastfeeding, so a nursling who took 30 minutes to nurse as a newborn may take only 10-15 minutes as a 4 month old. Older babies are more likely to have a predictable feeding pattern/routine, especially if they have a nap routine/schedule. I often help moms learn how to guide their baby (at least 2 months old) into an age-appropriate sleep routine and then baby naturally sets her own feeding routine around it. The more you focus on learning and responding to baby's feeding and sleep cues the first two months, the easier it is to identify their ideal routine later. (But if you need more guidance, consult The No-Cry Sleep Solution. It is the only book on routines that I recommend. Many other books that focus on schedules, including Babywise, are not compatible with successful breastfeeding for most women.)

One of the most important take-aways with your new understanding of milk storage capacity is not to compare you and your baby's feeding rhythm to other mothers and babies. Each mother/baby pair has a unique rhythm that should be respected and embraced, since doing so is the key to a truly happy, successful breastfeeding experience. The other take-away is that your baby is your best expert on setting a feeding rhythm, since s/he will naturally adapt a feeding pattern that fits his individual intake.
Further Reading
Breastfeeding Made Simple (great info on breastfeeding rhythms and storage capacity)